Embed Size (px)
Citation preview
Classes are Premature Optimization:
Prototypes in JavascriptJustin Love
http://pinboard.in/u:wondible/t:prototypal/http://pinboard.in/u:wondible/t:oop/
Outline
• OOP
• Classical
• Prototypal
• Objects in Javascript
• Patterns and performance
• Review
OOP?
class ____ {
...
}
object ____ {
...
}
Class Oriented?
class ____ {
...
}
OOP-or-
COP?
OOP
Those who do not remember history are condemned to repeat it.
George Santayana
(Chances are I’m repeating it right now.)
Alan Kay
3things
OOP
EncapsulationLocal
RetentionProtection
Hidingof State-process
Genericity
Commonly, PolymophisimAlan Kay spoke of Algebras
Extreme late binding
Messaging
Object decides how to react.
OOP
EncapsulationGenericityMessaging
Classes
Inheritance
“Five words
objectmessageclassinstancemethod
make up the vocabulary with which Smalltalk
is discussed.”
Smalltalk-80, The Language, p.51
Smalltalk 71727680
Classes
Inheritance
Metaclasses
Alan Kay2003
“So I decided to leave out inheritance as a built-in feature until I understood it better.”
Alan Kay2003
“[...] backslid towards Simula and did not replace the extension mechanisms with safer ones that were anywhere near as useful.”
Classical
Sketchpad
1963
Generalvs.
Specific
Simula-67
C++Javaetc.
Classes Instances
Segregation
Plato
Formvs.
Matter
Descriptionvs.
Representation
Classes Instances
Metaclass
“Class of classes”
RubyRuby Logo © 2006, Yukihiro Matsumoto
I’m not smart enough for Ruby’s
object system.
Peter DeutschThe Past, Present, and Future of Smalltalk
1989
“metaclasses have proven confusing to many users, and perhaps in the balance more confusing than valuable.”
Accidental Complexity
William of Ockham
“entia non sunt multiplicanda praeter necessitatem”
William of Ockham
“entities must not be multiplied beyond necessity”
Prototypal
Henry LiebermanOOPSLA 1986
http://web.media.mit.edu/~lieber/Lieberary/OOP/Delegation/Delegation.html
Using Prototypical Objects to Implement Shared Behavior in Object Oriented Systems
Self
1987
Abstractions
Objects
(Classes)
Objects
Abstractions?
one
one = Object.create(Object.prototype)
one two
two = Object.create(one)
one two
two = Object.create(one)
Beware ofmutable state!
P
one two three .....
one = Object.create(ptoto)two = Object.create(proto)
three = Object.create(proto)
YouAin’tGonnaNeed It
Objects in Javascript
What’s an object?
An object is a
Hash Table
An object is a
Hash TableMap
An object is a
Hash TableMap
Implementation detail
Map
a x
b y
c z
Array
0 x
1 y
2 z
Array
number value
Object
string value
Syntactic Sugar
object[‘string’]
object.string
Prototypes
Objects can be related
Reference
Every object has a
prototype
Prototype
What You’ve GotIt’s Prototype
Objects
ECMAScript Spec
[[Prototype]]
Mozilla
.__proto__
ECMAScript 5
Object.getPrototypeOf(instance)
Read
= x.b
Read
= x.a
Read
= x.toString
Write
x.a = “C”
Readback
= x.a
Compound Objects
“Classes”
new Class();
Syntatic Sugur
Leaky Abstraction
Object.create()
• ES5
• Firefox 4
• Safari 5
• Chrome 5
• IE 9
• http://kangax.github.com/es5-compat-table/
Object.create()
Object.create = function(o) {
function F() {};
F.prototype = (o || {});
return new F();
}
http://javascript.crockford.com/prototypal.html
P
one two three .....
one = Object.create(ptoto)two = Object.create(proto)
three = Object.create(proto)
Singleton
Singleton (in JS)
var singleton = {
...
};
Ex-Nihilo
“Out of Nothing”
Singleton: Self
clone = (self)
Prototypal Singleton
singleton.clone = function() {
return this;
};
Hard-core Singleton
function Singleton() {
return Singleton.prototype;
}
Near Miss
Near Miss
Near MissDay
Kin
Near Miss
var kin = day.clone("Kin");
Near Miss
clone: function(name) {
var o = Object.create(this);
o.name = name;
...
return o;
},
Near Miss
...
// independent existence.
o.scale = 0;
o.position = 0;
o.time = 0;
...
Nested Context
Nested Context
Like {block scope}.
(Or function scope in Javascript.)
Nested Context
under: function(path, f) {
var m = Object.create(this);
m.cd(path);
f(m);
},
Performance
Structured Memory
Programming as Experience:The Inspiration for Self
1995
Self runs
“2.3 times slower than optimized C++.”
Self includes: SmalltalkMario Wolczko
“all [sample] Smalltalk programs run faster in the the Self system, some significantly more so.”
Omega
1990Statically-typed prototypes
Design-Timevs.
Run-Time
Kevo
1993Concatative
‘Clone families’
Lisaac
2003Compiled.
44% slower to 17% fasterthan c.
http://www.lisaac.org/documentation/benchmarks
V8 Logo © 2006 Google
V82008
V8 Logo © 2006 Google
Generated Code
V8 Logo © 2006 Google
Hidden Classes
Javascript
1996
Javascript
Is not an Object-Oriented Programming Language
Genericity
PASS
Messaging
FAIL*Partial support in ES5 and Harmony
Encapsulation
FAIL*Work-around with closure.
Peter DeutschThe Past, Present, and Future of Smalltalk
1989
“inheriting implementation [...] tends to create difficulties in subsequent evolution and often reflects insufficient understanding.”
Copyvs.
Delegation
Shared Data
Shared Data
Shared Data
Shared Data
......
...
...
......
Seph
Stateless Delgation
http://olabini.com/blog/2010/07/preannouncing-seph/
Sparse Objects
Sparse Objects
Sparse Objects
new Disk('Minute',
unit.MS_S,
1,
T("seconds/minute"), {
colors: '#d22'
})
Sparse Objectsnew Disk('Solar Year',
unit.MS_D,
T("days/~month"),
12, {
colors: ['blue', 'green',
'orange', 'brown'],
...
Sparse Objects
...
majorNames: ['~January'...],
subDivide: 4,
major: 3*4,
median: 1*4,
...
Sparse Objects
...
render: function(context) {
context.save();
context.rotate(
6.28 * -9 / 365);
...
Flyweight
Flyweight
Flyweight
Flyweight
Flyweight
item: function(d) {
var i = Object.create(this);
i.dot = d;
return i;
},
Shared Behavior
Shared Behavior
Shared Behavior
Shared Behaviormint: function(
head, pattern, action) {
var my = this.dup();
my.head = head;
my.pattern = pattern;
my.action = action;
return my;
},
Shared Behavior
dup: function() {
return Object.create(this);
},
*
*
*
Prototype
Instances
Do I use class patterns?
YES
Do I use class patterns
for everything?
NO
a
Objects
Classes
a
Self
Smalltalk
Classesare aUsefulPattern
But notthe onlyPattern
Use Classes
Because You Want To
Use Classes
Because You Have To
Not
Review
History
OOP
Classical
Prototypal
Performance
Object
string value
Prototype
What You’ve GotIt’s Prototype
Objects
We’re Stuck with
Javascript
Learn How to Use It
Prototype
Instances
Shared Behavior
Shared Data
Singleton
Flyweight
Nested Context
Justin [email protected]
http://wondible.com
@wondible
http://pinboard.in/u:wondible/t:prototypal/http://pinboard.in/u:wondible/t:oop/
Questions?
